These predictions (the ones in science fiction) come from the imagination of the writters. There is no more power in them than there is in Tolkein's imagination or any other fiction writer.
However, in some cases, I believe there may be a 'self fulfilling prophecy' component. In the case of star trek, a number of scientists may have been inspired by some of the things they saw in the series. They grow up and work in that direction. Viola!! We have cell phones
As others have mentioned, people tend to remember the succesful predictions and not the ones that didn't work.
Right now I am sure you could make a prediction about what communication will be like in the future. If you are wrong, no one will remember. However, if you are correct, does that mean you had any sort 'power'. It just means they either had a little insight into possibilities or got lucky
